Linkage (redirected from Linkages)

linkage

In mechanical engineering, a system of solid, usually metallic, links (bars) connected to two or more other links by pin joints (hinges), sliding joints, or ball-and-socket joints to form a closed chain or a series of closed chains. When one link is fixed, the possible movements of the other links relative to the fixed link and to one another depend on the number of links and the number and types of joints. With four pin-connected links, for example, the links all move in parallel planes, and regardless of which link is fixed, the others move in a fixed way relative to the fixed link. With various relative lengths of the links, this four-bar linkage becomes a useful mechanism for converting uniform rotary to non-uniform rotary motion or continuous rotary to oscillatory motion. It is the most commonly used linkage mechanism in machine construction.

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linkage

See hypertext and linker.

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linkage

1. Engineering a system of interconnected levers or rods for transmitting or regulating the motion of a mechanism

2. Electronics the product of the total number of lines of magnetic flux and the number of turns in a coil or circuit through which they pass

3. Genetics the occurrence of two genes close together on the same chromosome so that they are unlikely to be separated during crossing over and tend to be inherited as a single unit

4. the fact of linking separate but related issues in the course of political negotiations

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linkage [′liŋ·kij]

(computer science)

In programming, coding that connects two separately coded routines.

(electromagnetism)

flux linkage

(genetics)

Failure of nonallelic genes to recombine at random in meiosis as a result of their being located within the same chromosome.

(mechanical engineering)

A mechanism that transfers motion in a desired manner by using some combination of bar links, slides, pivots, and rotating members.

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Linkage (genetics)

Failure of two or more genes to recombine at random as a result of their location on the same chromosome pair. Among the haploid products of a cell which has gone through meiosis, two genes located in the same chromosome pair remain in their two original combinations of alleles (“parental”) unless an odd number of exchanges of homologous segments occurred within the interval bounded by their loci. The incidence of exchanges of homologous segments at meiosis is roughly proportional to the length of the chromosome segment between two loci. The percentage of recombinants thus provides an estimate of this length and a basis for constructing gene maps on which linked loci are arranged in linear order and spaced out in proportion to the recombination percentages between them. See Meiosis

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Linkage (mechanism)

A set of rigid bodies, called links, joined together at pivots by means of pins or equivalent devices. A body is considered to be rigid if, for practical purposes, the distances between points on the body do not change. Linkages are used to transmit power and information. They may be employed to make a point on the linkage follow a prescribed curve, regardless of the input motions to the linkage. They are also used to produce angular or linear displacement. See Mechanism

If the links are bars the linkage is termed a bar linkage. A common form of bar linkage is one for which the bars are restricted to a given plane, such as a four-bar linkage. A commonly occurring variation of the four-bar linkage is the linkage used in reciprocating engines (see illustration). Slider C is the piston in a cylinder, link 3 is the connecting rod, and link 4 is the crank. (Link 1 is the fixed base, A and D are pivots, R is the length of the crank, L is the length of the connecting rod, and Θ denotes the angle of the crank.) This mechanism transforms a linear into a circular motion, or vice versa. The straight slider in line with the crank center is equivalent to a pivot at the end of an infinitely long link. See Pantograph

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Linkage 

a mechanism consisting of links joined together in lower kinematic pairs. Linkages can be plane or spatial. In plane linkages, the links make contact around a circumference (hinges, turning pairs) or along a line (sliding pairs). In spatial linkages, the links are joined over cylindrical or spherical surfaces (turning pairs) or over planes (sliding pairs). Link gears and slider-crank mechanisms are also considered to be linkages. In technical literature, linkages are often referred to as pin-connected mechanisms.

Linkages are simpler to fabricate, stronger, and more resistant to wear than cam and gear mechanisms. As a result, they are employed to transmit large forces in, for example, presses, forging machines, internal combustion engines, and loaders.

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Linkage 

(in Russian, sharnir), a movable connection between two bodies. In a cylindrical linkage, the relative movement of the two bodies is rotation about an axis; in a spherical linkage, the relative movement is rotation about a point.

A cylindrical linkage in a mechanism is called a rotary kinematic pair. It consists of a journal rotating in either a simple bearing or a rolling-contact bearing.

A spherical linkage in a mechanism is referred to as a spherical kinematic pair. It may be either a ball and socket or a ball bearing. Such a linkage is difficult to manufacture. Therefore, it is often replaced by a universal joint, which consists of two or three cylindrical linkages that are connected in tandem and whose axes of rotation intersect at a single point. Various modifications of the universal joint may be used instead of a spherical linkage; such modifications differ in the number of intermediate links and in the type of kinematic pairs formed by the intermediate links.

A linkage may be exposed or enclosed. An enclosed linkage is protected from dust or sand by a housing and is used in machinery that operates in air with a high dust content.

Linkages are used not only in machine mechanisms but also in building systems, such as trusses. In such systems, linkages are employed to relieve the components of bending stresses and to reduce thermal stresses.

N. I. LEVITSKII